• When released, the vapors initially move close to the ground, causing greater risk for exposure.

One of the worst disasters in U.S. history involving a form of ammonia occurred in April 1947 when a ship loaded with ammonium nitrate -- a solid fertlizer composed of ammonia and nitrogen -- caught fire while docked in Texas City, Texas, in April 1947. The fire caused an explosion that damaged more than 1,000 buildings, according to the website of the Texas Historical Association.

The blast ignited a fire on a second ship docked in Galveston Bay that was also loaded with ammonium nitrate. With most of the city's fire fighters killed in the first blast, the fire burned for 16 hours and caused another huge explosion. Volunteers fought to put out subsequent blazes.

The historical association said almost 400 people were killed and more than 175 were listed as missing. Only a few bodies in the dock area were even recovered.